1. Scope of the Invention
This invention relates to a process for the production of dimethoxycyclohexane. More particularly, it relates to an improved process for reaction of methanol with cyclohexanone in the presence of an acidic catalyst to form dimethoxycyclohexane ("DMC") in good yield and under conditions which facilitate the recovery of the product from the reaction mixture. As described in detail below, this is achieved by carrying out the reaction in the presence of a strongly acidic catalyst, and thereafter adding water as an azeotropic agent to separate unreacted cyclohexanone from the product by distillation, thereby recovering substantially pure DMC, and thus achieve significant economies over the prior art processes described below.
2. Description of the Prior Art
1,1-Dimethoxycyclohexane is an acetal which is a valuable intermediate in the production of perfumes and agricultural chemicals and which can be useful as dehydrating agent. Laboratory methods for the preparation of 1,1-dimethoxycyclohexane are unsatisfactory for commercial processes because they utilize expensive starting materials such as trimethylorthoformate [E. Taylor and C. Chiang, Synthesis, 467 (1977)] or methyl orthosilicate [B. Helferich and J. Hausen, Ber., 57B, 795 (1924)].
1,1-Dimethoxycyclohexane can be produced by the simple equilibrium controlled reaction of cyclohexanone with methanol under acidic conditions as follows: ##STR1## McCoy et. al. [J. Org. Chem., 22,1175 (1957); U.S. Pat. No. 2,822,402, Feb. 4, 1958] used methanolic HCl as the catalyst to produce 1,1-dimethoxycyclohexane. Their method suffers from low conversion of cyclohexanone and subsequent difficulty in separating the cyclohexanone from the product because of similar boiling points. Arashi et. al. [Jpn. Kokai 75, 111, 047, Sept. 1, 1975] improve the process by distilling with added hydrazine to facilitate the separation of cyclohexanone from 1,1-dimethoxycyclohexane. They also use drying agents to improve the conversion of cyclohexanone.
Canadian Pat. No. 651,644, while teaching the production of dimethoxycyclohexane, recovers this product, in part, by extracting unreacted cyclohexanone with large volumes of water, which is an inefficient method. Walker, U.S. Pat. No. 2,762,760, while teaching the formation of a known cyclohexanone/water azeotrope, does so in a process involving no ketals whatever and does not suggest or teach the advantages of using such an azeotrope in the preparation and purification of DMC.